5.1 Introduction
5.2
Hydrochemical aspects of the hydrological cycle
5.3 Major
characteristics of different types of resource
5.4 Contamination of water
resources
5.5 Tolerance limits
for humans and livestock
Although artificial pollution of natural water resources in tropical Africa is still comparatively rare, and limited to the vicinity of large urban centres and mining areas, the potable quality of water cannot be taken for granted, particularly since only a small percentage of the population has access to treated water. Pastoralists frequently share what water is available with their livestock and, although the latter have a higher tolerance to degree of contamination, water quality should always be considered as one of the limiting factors in developing a water resource.
The chemical, physical and biological characteristics of a water supply depend on many factors; for example, on the climatic, soil and geological conditions, and also on the activities of man within a drainage basin. The chapter discusses the main features concerning the natural quality of the resource and the ways in which sources can become contaminated by man's activities.
Whenever a potential water resource is being exploited, chemical and bacteriological analyses of water samples should be made as a standard measure. Not only does this give direct indications of the potability of the water, taking due account of possible seasonal effects, but it aids the future exploitation of the resource.
Chemical analyses are routinely performed by most public analysts and water laboratories. Analytical methods differ somewhat, but most of the field and laboratory procedures are essentially similar. Reference should be made to the standard procedures of the chosen laboratory and questions of non-standard requirements or additional analyses can then be discussed. Whereas samples for chemical analysis can easily be collected, stored and analysed retrospectively, samples for bacteriological analysis have to be carefully stored, refrigerated (chilled) and analysed within a short time of collection. Normally, the requirements for temperature control are that the sample is stored at or below 4°C to retard bacteriological decay. Analysis should preferably be carried out within 6 hours even when the above storage requirements are met. Otherwise, it must be accepted that the count of bacteria obtained will be lower than exists in the water source.
When collecting samples for chemical analysis, acidified and unacidified samples should be taken in order to preserve unstable cations, which may otherwise precipitate, and to prevent adsorption or plating onto the bottle surface.
To facilitate field reconnaissance surveys, portable test kits are available for measuring electrical conductivity, pH, major ions (CO32-, HCO3-, Cl-, SO4-, NO3-, Ca2+, Mg2+), total coliform and faecal coliform. The last of these is particularly important as an indicator of the presence of pathogens. It should be emphasised, however, that the presence of indicator organisms cannot be taken as a measure of the quantitative degree of faecal pollution or of the presence of pathogenic micro-organisms. If faecal contamination is indicated, then pathogens may also be present and professional advice should be sought.
Chemically pure water does not exist in nature. Rain droplets form on hygroscopic nuclei particles which have an affinity for water such as sodium chloride or sulphur trioxide - and these droplets have the ability to dissolve gases (such as carbon dioxide) from the atmosphere. Except in heavily industrialised areas, however, acidic rain is not a problem, and saline rainfall, although common in coastal zones and in arid continental areas where salt-laden dust is circulated in the atmosphere, still gives rise to relatively small concentrations of salt.
By far the most common source of the dissolved solids is in the passage of water through the soil and weathered mantle to bedrock. Chemical weathering causes the dissolution of minerals from rocks. The active agents are weak acids such as carbonic acid (formed by the dissolution of CO2 especially in the root zone) and humic acids (formed by the biological decomposition of organic matter). Another source of dissolved solids may be the oxidation of minerals present in the soils and rocks. Salts are added to infiltrating water from the soluble products of soil weathering. Evaporation tends to concentrate these salts in and above the root zone, leading to high surface salinities in arid areas where leaching by rainwater is not effective in diluting the salt solutions. Similarly, poorly drained areas and certain confined aquifers are highly susceptible to high saline concentrations.
The presence of evaporites in sedimentary sequences also leads to the enrichment of groundwater, with the specific ionic species derived from these minerals, e.g. CaSO4, NaCl.
As the depth of the aquifer increases, the rate of circulation of groundwater decreases. The greater retention times allow more minerals to be dissolved so that concentration tends to increase with depth. This can lead to a vertical stratification, with bicarbonates predominant in the upper zone and chlorides at depth. Evaporation from unconfined aquifers at the surface will tend to reverse this pattern in arid regions.
Because of the variety in which major ions can occur, it is sometimes convenient to group the common configurations into categories known as hydrochemical facies, and references may be found to such in hydrogeological texts. Hydrochemical facies can be defined as distinct zones which have anion and cation concentrations which can be described within certain composition categories (Freeze and Cherry, 1979). Thus, for example, one can refer to calcium-magnesium facies, calcium-sodium facies, sodium-calcium facies and sodium facies.
In stratified or mixed assemblages of unconsolidated sediments or rocks, groundwater can follow many different geochemical evolution paths, depending on the sequence of encounter, relative rates of mineral dissolution, mineral availability and solubility, presence of organic matter and bacteria, carbon dioxide conditions and temperature. In addition, a change in climate can cause a change in the rate of infiltration and leaching, or a change in the rate of evaporation. The chemical composition of groundwater, therefore, may well be a function of the palaeohydrogeology, in addition to the other variables. No attempt will be made to enter into the complex subject of genetic classification of groundwater in this report. Interested readers should refer to Freeze and Cherry (1979), Eriksson (1981), Schoeller (1977) and the numerous references contained in those texts.
5.3.1 Surface water
5.3.2 Lakes and swamps
5.3.3 Groundwater
Because of the short time of travel of surface runoff compared to groundwater, and the frequent removal of available minerals from the soil surface, streams and rivers normally contain far lower concentrations of dissolved solids than does groundwater. Exceptions occur wherever groundwater discharges into surface streams and forms a major component of the flow. In volcanic areas highly mineralised springs, often of high temperature, can produce great changes in the chemical composition of streamflow over short distances. During times when baseflow predominates, the concentration of dissolved solids can also be expected to rise considerably.
Stormflow has the shortest time of travel, but high velocities enable the runoff to remove and transport large quantities of suspended solids. These consist of particles of rock material ranging in size from large boulders to very fine clay particles, together with varying amounts of organic material. The total sediment yield of a drainage basin depends on a large number of variables, often grouped under 'rainfall erosivity' and 'soil erodibility' (ASCE, 1977). Catchment size has an influence because the rate of sediment movement attenuates as particles move from the erosion source into larger drainage basins.
Accelerated soil erosion, resulting from overcultivation, overgrazing and deforestation, will increase the total sediment load in streams and rivers. Often this can be gauged by measuring the suspended solids at different flows, so that a sediment-discharge curve can be constructed. When combined with a flow-duration curve, it is possible to integrate the total suspended sediment yield for a year. Unfortunately, the most difficult part of the sediment load to measure bed load - can be a significant proportion of the total sediment yield, particularly in semi-arid areas. Conventional estimates of 25% of total load can grossly underestimate bed load transport on steep catchments.
Figure 23 gives an indication of how sediment yield varies with catchment size (Edwards, 1979). The high yields recorded in the USA reflect the measurements from loess-covered catchments where easily erodible, fine particles abound. Crystalline rocks are better represented in the curve of Fleming (1969). Highly turbid water resulting from flash floods is usually organically polluted, but high dilution rates often render it less of a threat than the low flows. Retention and storage will allow much of the suspended sediment to be deposited, but clay particles can remain in suspension for long periods, cutting down the penetration of ultraviolet, bacteria-killing sunlight.
Figure 23. Suspended sediment yield in relation to catchment area.
Bacteria and other micro-organisms play a vital role in the self-purification ability of a river, because they biologically break down the organic matter present into simpler inorganic substances. In doing so, however, they exert an oxygen demand on the water. Where excessive quantities of organic matter are present, as for instance below the outfall of a sewage discharge, the increased bacterial activity can seriously deplete the oxygen content to below that which can sustain aquatic life (4 mgO2/l). Where severe pollution occurs, the river can become devoid of oxygen and is termed anaerobic. Such rivers become foul smelling.
The biochemical oxygen demand (BOD) of a water body is a measure of the oxygen consumed by bacteria in breaking down organic material present in the water.
The standard test is conducted on samples incubated at 20°C for a period of 5 days (BOD5). In hot climates the test requires a refrigerated incubator. A much simpler and more rapid test (completed in 2 ½ hours) is the determination of chemical oxygen demand (COD), which is a measure of the oxygen required to break down the organic material supplied by strong chemical oxidants.
Both tests - COD and BOD - measure the stress or 'load' a quantity of organic waste puts on a receiving water. Pollution load is the amount of dissolved oxygen that organic material will remove from water while being converted to carbon dioxide and water by microorganisms. When wastewater contains only readily oxidisable organic material, and nothing that is toxic to bacteria, COD test results are a good estimate of BOD values.
Natural retention of surface waters in lakes and swamps leads to a dramatic reduction in suspended solids. Swamps often filter finer particles from suspension reducing the turbidity. Against these beneficial effects, high evaporation and transpiration rates lead to a concentration of dissolved minerals and, under certain conditions, organic pollution can increase. It is generally considered that in most natural water bodies bacteriological concentrations are reduced as a result of the unfavourable bacteriological environment (see Powell, 1964). In turbid lakes and swamps, however, not only are bacteria adsorbed on the surface of suspended clay minerals but, given a supply of oxygen, a source of assimilable organic carbon and high temperatures, the natural decay of bacteria will be inhibited and, in this very favourable environment, bacteria will multiply rapidly.
Prolific algal growth is a common nuisance where dissolved nutrients are present (N. P). High concentrations of blue-green algae, notably Microcystis and Anabaena in water consumed by stock, have been reported as the cause of fatal poisoning in many instances (Gorham, 1964, Powell, 1964). In slow-moving waters vegetational pollution is a serious problem. The water hyacinth (Eichornia crassipes), Kariba weed (Salvinia molesta) and parrot's-feather (Myriophyllum aquaticum) are among the species of aquatic weed which are found in tropical Africa. They are notorious for their spectacular capacity for explosive population growth. Some are native species and some, like the examples cited, have been introduced from South America. All have the capacity to reduce flow, to choke small lakes, to reduce oxygen levels and water quality and to provide breeding places for mosquitoes and for the snails which are the intermediate hosts of schistosomiasis.
Groundwater is generally free from suspended solids and objectionable colour but, as has been discussed above, it contains higher concentrations of dissolved solids than surface water in the same locality. Preliminary indications of total dissolved solids can be obtained from simple electrical conductivity (EC) tests made in the field. Chemically pure water is a poor electrical conductor whereas highly mineralised water is a very good conductor. EC, measured in microsiemens per centimetre, therefore, is a rapidly obtained measure of total dissolved solids. EC is normally 1.4 to 1.8 times the total dissolved solids concentration in mg/l, which implies that readings of 3000 microsiemens/cm will indicate a concentration in excess of the WHO recommended maximum levels (see below).
The pH of groundwater is also a rapidly obtained measure and indicates whether the water is acidic (pH < 7) or alkaline (pH > 7). Groundwater generally has a pH within the range 6 to 9. Acidic waters are 'aggressive' and lead to the solution of iron and manganese, both of which impart an unpleasant and unpalatable taste.
Where mineral deposits lie within the zone of circulating water, toxic minerals such as selenium, zinc, arsenic, lead, fluorides and nitrates may be taken into solution. Under natural conditions the mineralised zone may be surrounded by an aureole of contaminated water. Pumping from a nearby well or borehole can lead to water from the zone of contamination being drawn towards the abstraction point. As this type of mineralisation may not be obvious when water is first tested for chemical quality, there is merit in periodic resampling to monitor water chemistry changes, especially where there are indications of the presence of toxic minerals in the area.
Deep sedimentary basins in arid areas are often the source of fossil or connate water. These types of groundwater have little or no circulation and are usually of high salinity. Sedimentary deposits on the arid border between Kenya and Somalia contain fossil water with more than 10 000 mg/l of total dissolved solids. Mesozoic sandstones of North Africa, on the other hand, have fresh water which was stored during the Pleistocene epoch and are a good example of exploitable fossil water.
Contamination of water resources can occur naturally over very long periods of time, particularly in response to climatic change. But the major cause of contamination by far is man's activity and, in this case, contamination can occur rapidly and dramatically.
Surface waters can be choked with sediment as a result of accelerated soil erosion caused by destruction of protective vegetation. Noxious aquatic weeds, once introduced into a region, can be rapidly spread by birds, animals and humans.
Fortunately, the major sources of surface water pollution - urban and industrial effluent are absent in the pastoral regions, but local concentrations of nitrates due to poor dilution of untreated organic waste are a hazard to livestock and humans (infantile cyanosis), particularly during the low-flow season. Nitrates are usually reduced in surface waters by denitrifying bacteria, but water containing large amounts of decaying organic material (e.g. manure) may be very high in nitrate (< 200 mg NO3/l) and so may constitute a potential danger.
Contaminated drinking water is a significant factor in the spread of infectious, water-related diseases. Lack of water for personal hygiene leads to the increased possibility of transmission of disease by a variety of faecal - oral routes. Both from a human and livestock point of view, reliance on polluted surface water supplies can lead to a high incidence of water-based diseases (bilharzia, river blindness, schistosomiasis, Guinea worm) and insect-vector, water-related diseases (trypanosomiasis, malaria, yellow fever, dengue and onchocerciasis). In considering the provision of additional water sources, therefore, their effect on the possible spread of disease must be taken into account.
Micro-organisms and spores of diseases common in livestock may also be present in water supplies. Prevention of contamination of livestock drinking water with urine, faeces and carcasses is especially important if the presence of a. water-borne or water-associated livestock disease is suspected. Among bacterial infections, leptospirosis and salmonella are common and both affect humans. Table 10 lists a number of significant viral diseases which may be associated with stock drinking water (Australian Water Resources Council, 1974).
A number of livestock parasites, including protozoa, flatworms and roundworms, spend part of their life cycle in water. Faecal contamination is the usual means of introduction into the water.
It is recommended that the faecal coliform level should be used as an indicator of pathogenic organisms. The mean monthly faecal coliform count should be less than 1000/100 ml with a maximum in any single count of 5000/100 ml (Australian Water Resources Council, 1974).
Table 10. Significant viral diseases which may be associated with stock drinking water.
| Picornavirus infections, including: | |
| Foot-and-mouth disease | |
| Teschen/Talfan disease | |
| Avian encephalomyelitis | |
| Encephalomyocarditis | |
| Swine vesicular disease | |
| Parvovirus infections | |
| Adenovirus infections, including infectious canine hepatitis | |
| Rinderpest virus | |
| Swine fever (hog cholera) | |
| African swine fever | |
| Mucosal disease | |
Groundwater is normally of high bacteriological quality since the soil usually affords the underlying aquifer a considerable degree of protection against contamination. Local contamination of a groundwater source usually occurs if inadequate provision is made to prevent the ingress of polluted surface water around the borehole casing or well lining. If thorough attention is paid to grouting the casing or lining, and an adequate concrete apron is provided above ground, this common route of bacteriological contamination can be avoided. Shallow wells are more susceptible to lateral movement of contaminated water from sources of organic pollution such as pit latrines, particularly in areas of high water tables. In consolidated porous soils, 2 to 3 m of vertical separation between latrine bases and the water table and 50 m of lateral separation are normally sufficient to prevent gross pollution of shallow wells from pit latrines or livestock pens. In areas of high permeability or where the soils overlie fractured rock, however, the lateral separation may have to be increased to 100 m or more.
Cattle dips using arsenical acaricides are also a potential source of contamination, particularly since they are normally sited very close to a water source. Separation of the dip from the borehole or a change to more biodegradable, organophosphorus compounds are measures to be strongly recommended.
Mention has already been made of the possibility of drawing in contaminated water from mineralised aureoles during pumping. Care must also be taken in the presence of saline aquifers not to overpump a borehole, thus causing intrusion of the highly mineralised water into the fresh aquifer. This problem commonly arises in coastal aquifers, but in general only motorised boreholes will be capable of drawing off sufficient water to cause saline intrusions.
Within certain limits, the presence of minerals in drinking water is beneficial. In arid regions body electrolytes can be rapidly depleted by perspiration, and a constant intake of salts is required.
Drinking water standards for livestock may be less stringent than those for humans. Where a single water source serves both, the tolerance levels of the human body are obviously most important. The standards set by international bodies such as the WHO are extremely conservative and designed more for western industrialised nations where treatment of water is the norm. In tropical developing countries, not only are the bacteriological standards recommended by WHO almost impossible to attain in untreated drinking water supplies serving rural areas, but they also occasionally act in a negative way. Overzealous health officials may condemn a mildly contaminated water point as unfit to drink because, say, it contains 50 faecal coliforms per 100 ml and, thus, force the consumer to use alternative traditional sources, possibly containing 1000 or more per 100 ml.
Table 11 gives the WHO recommended standards for drinking water as laid down for Europe in 1971 and the rest of the world in 1972. Table 12 lists trace element and compound standards according to three categories of limits: recommended, mandatory and unofficial. Schoeller acknowledges that these standards cannot be universally applied, particularly with regard to the major anions and cations and total dissolved solids. Acceptable upper limits will depend on the climate, the total dietary intake and the work being done by the user. If no other water is available, the body adjusts to high levels of salinity. Cases have been recorded in South Australia of families living for several months on water having total salinity in excess of 5000 mg/l (Ward, 1946).
Table 13 gives the standards for drinking water in arid regions suggested by Schoeller (1977). These are based on the physiological tolerance of the user and the acceptability of the water as regards taste. Schoeller points out that it is the element with the highest value. in relation to the limits which defines the water's suitability, rather than the value of the total dissolved solids.
Recommended concentration limits for livestock according to different authorities are given in Tables 14 and 15. There are differences between the values given by the agencies, but they serve as useful guidelines when developing new sources. It is clear that tolerance to total dissolved solids varies widely, and very high concentrations are acceptable in very hot, dry climates, or for short periods of time.
Bacteriological standards for animals are difficult to assess because of the varying degree of immunity to certain infections or parasitic diseases which indigenous livestock may possess. Limits for parasites and pathogens must be based on epidemiological evidence obtained from specific localities. A discussion of this topic is outside the scope of this report. It must be emphasised, however, that faecal pollution of water supplies by animals is potentially pathogenic to humans as well, and that the interaction between human and livestock populations using the same water source can produce harmful effects.
Table 11. World Health Organisation and international water quality standards.
European standards |
International standards |
||
| Biologya | |||
| Coliform bacteria | Nil | Nil | |
| Escherichia coli | Nil | Nil | |
| Streptococcus faecalis | Nil | Nil | |
| Clostridium perfringens | Nil | Nil | |
| Virus | Less than 1 plaque-forming unit per litre per examination in 10 litres of water | ||
| Microscopic organisms | Nil | ||
| Radioactivity | |||
| Overall a radioactivity | <3 pCi/l | <3 pCi/l | |
| Overall b radioactivity | <30 pCi/l | <30 pCi/l | |
| Chemical elements/compounds | |||
| Pb | <0.1 mg/l | <0.1 mg/l | |
| As | <0.05 | <0.05 | |
| Se | <0.01 | <0.01 | |
| Hexavalent Cr | <0.05 | <0.05 | |
| Cd | <0.01 | <0.01 | |
| Cyanides (in CN) | <0.05 | <0.05 | |
| Ba | <1.00 | <1.00 | |
| Cyclic aromatic hydrocarbon | <0.20 | ||
| Total Hg | <0.01 | <0.01 | |
| Phenol compounds (in phenol) | <0.001 | <0.001-0.002 | |
| NO3- recommended | <50 | ||
| acceptable | 50-100 | ||
| not recommended | >100 | ||
| Cu | <0.05 | 0.05-1.5 | |
| Total Fe | <0.1 | 0.10-1.0 | |
| Mn | <0.05 | 0.10-0.5 | |
| Zn | <5 | 5-15 | |
| Mg if SO4 >250 mg/l | <30 | <30 | |
| if SO4<250 mg/l | <125 | <125 | |
| SO42- | <250 | 250-400 | |
| H2S | 0.05 | ||
| C recommended | <200 acceptable | <600 | |
| NH4- | <0.05 | ||
| Total hardness | 2-10 meq/l | 2-100 meq/l | |
| Ca | 75-200 mg/l | 75-200 mg/l | |
F In the case of fluorine the limits depend upon air temperature:
Mean annual maximum day-time temperature (°C) |
Lower limit (mg/l) |
Optimum (mg/l) |
Upper limit (mg/l) |
Unsuitable (mg/l) |
| 10-12 | 0.9 | 1.2 | 1.7 | 2.4 |
| 12.1-14.6 | 0.8 | 1.1 | 1.5 | 2.2 |
| 14.7-17.6 | 0.8 | 1.0 | 1.3 | 2.0 |
| 17.7-21.4 | 0.7 | 0.9 | 1.2 | 1.8 |
| 21.5-26.2 | 0.7 | 0.8 | 1.0 | 1.6 |
| 26.3-32.6 | 0.6 | 0.7 | 0.8 | 1.4 |
a
No 100 ml sample to contain E. coli or more than 10 coliforms.
Source: Schoeller (1977).
Table 12. Water quality criteria for trace elements and compounds.
Element/compound |
Comment |
Recommended limit (mg/l) |
Mandatory limit (mg/l) |
Unofficial limit (mg/l) |
| Alkyl benzine sulphonate (ABS) | 0.5 | |||
| Arsenic (As) | Serious cumulative systemic poison; 100 mg usually causes severe poisoning. | 0.01 | 0.05 | |
| Antimony (Sb) | Similar to As but less acute. Recommended limit 0.1 mg/l, routinely below 0.05 mg/l over long periods below 0.01 mg/l. | 0.05 | 0.05 | |
| Barium (Ba) | Muscule (including heart) stimulant. Fatal dose is 550-600 mg as chloride. | 1 | ||
| Beryllium (Be) | Poisonous in some of its salts in occupational exposure. | none | ||
| Bismuth (Bi) | A heavy mineral in the arsenic family - avoid in water supplies. | none | ||
| Boron (B) | Ingestion of large amounts can affect central nervous system. | 1 | 5 | 1 |
| Cadmium (Cd) | 13-15 ppm in food has caused illness. | 0.01 | ||
| Carbon chloroform extract (CCE) | At limit stated, organics in water are not considered a health hazard. | 0.200 | ||
| Chloride (Cl-) | Limit set for taste reasons. | 250 | ||
| Chromium (hexavalent) | Limit provides a safety factor. Carcinogenic when inhaled. | 0.05 | ||
| Cobalt (Co) | Beneficial in small amounts; about 7 m g/day. | none | ||
| Copper (Cu) | Body needs copper at a level of about 1 mg/day for adults; not a health hazard unless ingested in large amounts. | 1.0 | ||
| Cyanide (CN-) | Rapid fatal poison, but limit set provides safety factor of about 100. | 0.01 | 0.20 | |
| Fluoride (F-) | Beneficial in small amounts; dose above 2250 mg can cause death. | 0.7-1.2 | 1.4-2.4 | |
| Iron (Fe) | 0.3 | |||
| Lead (Pb) | Serious cumulative body poison. | 0.05 | ||
| Manganese (Mn) | 0.05 | |||
| Mercury (Hg) | Continued ingestion or large amounts can damage brain and central nervous system. | 0.005 | ||
| Molybdenum (Mo) | Necessary for plants and ruminants. Excessive intakes may be toxic to higher animals; acute or chronic effects not well known. | none | ||
| Nickel (Ni) | May cause dermatitis in sensitive people, doses of 30-73 mg of NiSO4 6H2O have produced topic effects. | none | ||
| Nitrate (NO3-) | Excessive amounts can cause methemoglobinemia (blue baby) in infants. | 45 | ||
| Radium (Ra-226) | A bone-seeking, internal alpha emitter that can destroy bone marrow. | 3 pc/l | ||
| Selenium (Se) | Toxic to both humans and animals in large amounts. Small amounts may be beneficial. | 0.01 | ||
| Silver (Ag) | Can produce irreversible, adverse cosmetic changes. | 0.05 | ||
| Sodium (Na) | A beneficial and needed body element, but can be harmful to people with certain diseases. | 200 | ||
| Strontium-90 | A bone-seeking internal beta emitter. | 10 pc/l | ||
| Sulphate (SO42-) | 250 | |||
| Zinc (Zn) | Beneficial in that a child needs 0.3 mg/kg/day; 675-2280 mg/l may be an emetic. | 5 |
Source: Schoeller (1977).
Table 13. Water quality standards for arid regions.
Suitability for permanent supply |
||||
good |
fair |
moderate |
poor |
|
| Colour | colourless | colourless | ||
| Turbidity | clear | clear | ||
| Odour | odourless | hardly perceptible | slight | slight |
| Taste at 20°C | none | perceptible | pronounced | unpleasant |
| Total dissolved solids (mg/l) | 0-500 | 500-1000 | 1000-2000 | 2000-4000 |
| EC(m S/cm) | 0-800 | 800-1600 | 1600-3200 | 3200-6400 |
| Na (mg/l) | 0-115 | 115-230 | 230-460 | 460-920 |
| Mg (mg/l) | 0-30 | 30-60 | 60-120 | 60-120 |
 |
0-5 | 5-10 | 10-20 | 20-40 |
| Cl (mg/l) | 0-180 | 180-360 | 360-710 | 710-1420 |
| SO4 (mg/l) | 0-150 | 150-290 | 290-580 | 580-1150 |
Source: Schoeller (1977).
Table 14. Recommended mineral concentration limits for livestock.
Element |
Derived maximum working level (mg/l) |
| Arsenic (as As) | 1.0 |
| Boron (as B) | |
| Cadmium (as Cd) | 0.01 |
| Calcium (as Ca) | 1000 |
| Chromium (as Cr) | 1 to 5 |
| Copper (as Cu) | 0.5 to 2.0 |
| Fluoride (as F) | 2 |
| Iron (as Fe) | 10 |
| Lead (as Pb) | 0.5 |
| Magnesium (as Mg) | 250 to 500 |
| Mercury (as Hg) | 0.002 |
| Molybdenum (as Mo) | 0.01 |
| Nitrogen (as NO3) | 90 to 200 |
| Selenium (as Se) | 0.02 |
| Sulphur (as So42-) | 1000 |
| Zinc (as Zn) | 20 |
Livestock |
Maximum total dissolved salts |
Maximum magnesium |
|
Western Australia |
Victoria |
Australia |
|
| Poultry | 2900 | 3500 | |
| Pigs | 4300 | 4500 | |
| Horses | 6400 | 6000 | 250 |
| Dairy cows | 7100 | 6000 | 250 |
| Beef cattle | 10 000 | 7000 | 400 |
| Sheep on dry feed | 13 000 | 14 000 | 500 |
| Ewes with lambs | 10 000 | 4500 | 250 |
| Ewes in milk | 10 000 | 6000 | |
Table 15. Key water quality criteria for livestock.
Substance |
Upper limit |
| Total dissolved salts (mg/l) | 10 000a |
| Radionuclides (pCi/l) | |
| 90Sc | 10 |
| 255Ra | 3 |
| Activity | 1000 |
| Chemicals (mg/l) | |
| MgSO4 | 2050 |
| NaCI | 2000 |
| SO42- | 1000 |
| As | 0.05 |
| Cd | 0.01 |
| Cr | 0.05 |
| F | 2.40 |
| Pb | 0.05 |
| Se | 0.01 |
| Organic substances | |
| Algae (water bloom) | -b |
a
Depending upon animal species and ionic composition of the water.
b Avoid abnormally heavy growth of blue-green algae. Parasites and pathogens conform to epidemiological evidence.
